Berkeley Software Distribution

BSD redirects here; for other uses see BSD (disambiguation).

Berkeley Software Distribution (BSD) is the UNIX derivative distributed by the University of California, Berkeley starting in the 1970s. The name is also used collectively for the modern descendants of these distributions.

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A rendering of the BSD daemon by Poul-Henning Kamp



PDP-11 beginnings

The earliest distributions of Unix from Bell Labs in the 1970s included the source code to the operating system, allowing researchers at universities to modify and extend Unix. The first Unix system at Berkeley was a PDP-11 installed in 1974, and the computer science department used it for extensive research thereafter.

Other universities became interested in the software at Berkeley, and so in 1977 Bill Joy, then a graduate student at Berkeley, assembled and sent out tapes of the first Berkeley Software Distribution (1BSD). 1BSD was an add-on to Sixth Edition Unix rather than a complete operating system in its own right; its main components were a Pascal compiler and Joy's ex line editor.

The Second Berkeley Software Distribution (2BSD), released in 1978, included updated versions of the 1BSD software as well as two new programs by Joy that persist on Unix systems to this day: the vi text editor (a visual version of ex) and the C shell.

Later releases of 2BSD contained ports of changes to the VAX-based releases of BSD back to the PDP-11 architecture. The most recent release, 2.11BSD, was first released in 1992, with maintenance updates continuing until 2003.

VAX versions

A VAX computer was installed at Berkeley in 1978, but the port of Unix to the VAX architecture, UNIX/32V, did not take advantage of the VAX's virtual memory capabilities. The kernel of 32V was largely rewritten by Berkeley students to include a virtual memory implementation, and a complete operating system including the new kernel, ports of the 2BSD utilities to the VAX, and the utilities from 32V was released as 3BSD at the end of 1979.

The success of 3BSD was a major factor in the Defense Advanced Research Projects Agency's decision to fund Berkeley's Computer Systems Research Group, which would develop a standard Unix platform for future DARPA research. CSRG released 4BSD, containing numerous improvements to the 3BSD system, in October 1980.

4.1BSD (June 1981) was a response to criticisms of BSD's performance relative to the dominant VAX operating system, VMS. The 4.1BSD kernel was systematically tuned up by Bill Joy until it could perform as well as VMS on several benchmarks. (The release was not called 5BSD to avoid confusion with AT&T's UNIX System V release.)

4.2BSD would take over two years to implement and contained several major overhauls. Before its official release came three intermediate versions: 4.1a incorporated a modified version of BBN's preliminary TCP/IP implementation; 4.1b included the new Berkeley Fast File System, implemented by Marshall Kirk McKusick; and 4.1c was an interim release during the last few months of 4.2BSD's development.

The official 4.2BSD release came in August 1983. It was notable as the first version released after the 1982 departure of Bill Joy to co-found Sun Microsystems; Mike Karels and Marshall Kirk McKusick took on leadership roles within the project from that point forward. On a lighter note, it also marked the debut of BSD's daemon mascot in a drawing by McKusick that appeared on the cover of the printed manuals distributed by USENIX.

4.3BSD releases

4.3BSD was released in June 1986. Its main changes were to improve the performance of many of the new contributions of 4.2BSD that had not been as heavily tuned as the 4.1BSD code. Prior to the release, BSD's implementation of TCP/IP had diverged considerably from BBN's official implementation. After several months of testing, DARPA determined that the 4.2BSD version was superior and would remain in 4.3BSD. (See also History of the Internet.)

After 4.3BSD, it was determined that BSD would move away from the aging VAX platform. The Power 6/32 platform (codenamed "Tahoe") developed by Computer Consoles, Incorporated seemed promising at the time, but was abandoned by its developers shortly thereafter. Nonetheless, the 4.3BSD-Tahoe port (June 1988) proved valuable as it led to a separation of machine-dependent and machine-independent code in BSD which would improve the system's future portability.

Until this point, all versions of BSD had incorporated proprietary AT&T Unix code and therefore required licenses from AT&T for their use. Source code licenses had become very expensive by this point, and several outside parties had expressed interest in a separate release of the networking code, which had been developed entirely outside AT&T and would not be subject to the licensing requirement. This led to Networking Release 1 (Net/1), which was made available to non-licensees of AT&T code and was freely redistributable under the terms of the permissive BSD license. It was released in June 1989.

4.3BSD-Reno came in early 1990. It was an interim release during the early development of 4.4BSD, and its use was considered a "gamble", hence the naming after the gambling center of Reno, Nevada.

Net/2 and legal troubles

After Net/1, BSD developer Keith Bostic proposed that more non-AT&T sections of the BSD system be released under the same license of Net/1. To this extent, he started a project to reimplement most of the standard Unix utilities without using the AT&T code. For example, vi, which had been based on the original Unix version of ed, was rewritten as nvi (new vi). Within eighteen months, all the AT&T utilities had been replaced, and it was determined that only a few AT&T files remained in the kernel. These files were removed, and the result was the June 1991 release of Net/2, a nearly complete operating system that was freely redistributable.

Net/2 was the basis for two separate ports of BSD to the Intel 80386 architecture: the free 386BSD by William Jolitz and the proprietary BSD/OS by Berkeley Software Design (BSDi). 386BSD itself was short-lived, but became the initial code base of the NetBSD and FreeBSD projects that were started shortly thereafter.

BSDi soon found itself in legal trouble with AT&T's UNIX Systems Laboratories subsidiary, then the owners of the System V copyright and the Unix trademark. The USL v. BSDi lawsuit was filed in 1992 and led to an injunction on the distribution of Net/2 until the validity of USL's copyright claims on the source could be determined.

The lawsuit slowed development of the free-software descendants of BSD for nearly two years while their legal status was in question, and as a result systems based on the Linux kernel, which did not have such legal ambiguity, gained greater support. Linux and 386BSD began development at about the same time, and Linus Torvalds has said that if there had been a free Unix-like operating system on the 386 at the time, he likely would not have created Linux. Although it is debatable exactly what effect that would have had on the software landscape since, there is little doubt that it would have been substantial.

4.4BSD and descendants

The lawsuit was settled in January 1994, largely in Berkeley's favor. Of the 18,000 files in the Berkeley distribution, only 3 had to be removed and 70 modified to show USL copyright notices. A further condition of the settlement was that USL would not file further lawsuits against users and distributors of the Berkeley-owned code in the upcoming 4.4BSD release.

In June 1994, 4.4BSD was released in two forms: the freely redistributable 4.4BSD-Lite contained no AT&T source, whereas 4.4BSD-Encumbered was available, as earlier releases had been, only to AT&T licensees.

The final release from Berkeley was 1995's 4.4BSD-Lite Release 2, after which the CSRG was dissolved and development of BSD at Berkeley ceased. Since then, several distributions based on 4.4BSD (such as FreeBSD, OpenBSD, and NetBSD) have been maintained.

In addition, the permissive nature of the BSD license has allowed many other operating systems, both free and proprietary, to incorporate BSD code. For example, Microsoft Windows has used BSD-derived code in its implementation of TCP/IP and bundles recompiled versions of BSD's command line networking tools with its current releases.


BSD pioneered many of the advances of modern computing. Berkeley's Unix was the first to include library support for the Internet Protocol stacks, Berkeley sockets. By integrating sockets with the UNIX operating system file descriptors, users of their library found it almost as easy to read and write data across the network, as it was to put data on a disk. The AT&T laboratory eventually released their own STREAMS library, which incorporated much of the same functionality in a software stack with better architectural layers, but the already widely-distributed sockets library, together with the unfortunate omission of a function call for polling a set of open sockets (an equivalent of the select call in the Berkeley library), made it difficult to justify porting applications to the new API.

Today, it continues to be used as technology testbed by academic organizations, as well as high-technology examples in a lot of commercial and free products. It is increasingly being used on embedded devices as well. The general quality of its source code design and clean writing, as well as its documentation (especially reference manual pages, commonly referred to as "man pages"), make such systems a heaven for programmers.

Many corporations use BSD derived code while being able to maintain their intellectual property (IP) because of the versatility of the BSD license, which is less restrictive than the GNU General Public License used by many other free software such as the Linux and GNU projects. This also means that you may be owning hardware internally running parts of BSD software without knowing it. Try looking for signs of "University of California, Berkeley" in the documentation of products, in the static data sections of binaries and ROMs, or as part of the "about" available through the user interface frontend of many products. Surprise (or lack thereof) might ensue.

It is an interesting fact that BSD operating systems can run native software of several other operating systems on the same architecture, using binary compatibility. This, much faster than emulation, allows for instance to run applications intended for Linux on a BSD operating system at full speed. This makes BSDs not only suitable for server environments, but also for workstation ones, considering the increasing availability of commercial or closed-source software for Linux. It also allows to migrate old commercial software which only used to run on commercial UNIX platforms to a modern BSD operating system, while retaining functionality of the previous system until it can fully be replaced by a better alternative.

Finally the BSD operating systems support some of the common IEEE, ANSI, ISO, and POSIX standards while retaining most of the traditional BSD behavior.

BSD derivatives/distributions

The different BSD operating systems are targeted in a wide array of systems for different purposes and uses. Many BSD installations though are common in government facilities. Though many all the following BSDs have features found in other systems, each BSD develops a reputation for being excellent in specific tasks such as performance and security

  • DragonFly BSD is the newest of the BSDs, and is still in its early stages of development. Dragonfly BSD has a reputation in extremely large SMP systems as well as network clusters.
  • FreeBSD is known for its user friendliness and excellent performance among the BSDs, due to its commitment to running in just a few microprocessor architectures, such as i386. It was recently ported to other architectures such as PowerPC. FreeBSD has a reputation in running i386 servers.
  • NetBSD is known for its portability among the BSDs, running in as many as 54 different platforms. It runs in a diverse array of systems that include small embedded and handheld devices, all the way up to large server farms. NetBSD is also used in the International Space Station. NetBSD has a reputation in small embedded devices as well as dedicated and fixed tasked machines and other applications.
  • OpenBSD is known for cryptography and security among the BSDs. Security features such as OpenSSH were pioneered in OpenBSD. OpenBSD has a reputation in running security demanding machines.

Most BSDs, however, can fulfill the roles of other BSDs.


Like AT&T Unix, the BSD kernel is monolithic, meaning that device drivers in the kernel run in privileged mode, as part of the core of the operating system. Early versions of BSD were used to form Sun Microsystems' SunOS, founding the first wave of popular Unix workstations.

Comparison of BSDs and Linux

See FreeBSD and Linux.

BSD descendants

Current Unix-like operating systems that descend from BSD include:

See also

External links

Further reading

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